Friction stir welding method

Abstract

A friction stir welding method which permits advantageous production of a product which has a sound welded area without joint defects, by joining together two members formed of the same material or respective different materials selected from a cast aluminum alloy and 2000 series, 4000 series, 5000 series and 7000 series aluminum alloys which are considered difficult to be joined together by the friction stir welding method. An initiation tab member formed of a 1000 series, 3000 series, 6000 series or 8000 series aluminum alloy is disposed in abutting contact with end faces of joining portions of first and second members (in an abutting part), on the side of initiation of the welding operation, and the friction stir welding operation is performed by moving a probe of a rotary tool through the initiation tab member into the joining portions of the two members.

The invention claimed is: 
     
       1. A friction stir welding method comprising:
 joining together joining portions of a first member and a second member by a friction stir welding operation performed by moving a probe of a rotary tool in a welding direction, while rotating said probe in the form of a rod by rotation of said rotary tool together with two shoulder members which are provided on said probe so as to be spaced apart from each other by a predetermined distance in an axial direction of said probe, and applying a pressure to said joining portions through said two shoulder members, wherein said first and second members are formed of the same material or respective different materials selected from a group consisting of a cast aluminum alloy and 2000 series, 4000 series, 5000 series and 7000 series aluminum alloys; 
 disposing an initiation tab member consisting of a 1000 series, 3000 series, 6000 series or 8000 series aluminum alloy in abutting contact with end faces of said joining portions of said first and second members on the side of initiation of said friction stir welding operation wherein said initiation tab member is a planar member having a length not shorter than four times a diameter of said shoulder members, in the direction of welding by the rotary tool, and a width not shorter than twice the diameter of said shoulder members, in a direction perpendicular to the direction of welding; and 
 moving said probe of said rotary tool into said joining portions of said first and second members through said initiation tab member to perform the friction stir welding operation with respect to said joining portions wherein a diameter of said probe of said rotary tool is not smaller than twice a thickness of said initiation tab member. 
 
     
     
       2. The friction stir welding method according to  claim 1 , wherein said joining portions of said first and second members are butted on each other to provide an abutting part, and said friction stir welding operation is performed with respect to the abutting part. 
     
     
       3. The friction stir welding method according to  claim 1 , wherein said joining portions of said first and second members are superposed on each other, and said friction stir welding operation is performed with respect to an overlapping part in which the joining portions are superposed on each other. 
     
     
       4. The friction stir welding method according to  claim 1 , wherein said rotary tool is a bobbin tool in which said two shoulder members are fixedly provided on said probe, with the predetermined distance therebetween. 
     
     
       5. The friction stir welding method according to  claim 1 , wherein said rotary tool is a self-reacting tool in which one of said two shoulder members is fixed to said probe, and the other of said two shoulder members is configured so as to be movable in the axial direction of said probe, so that said distance between said two shoulder members can be changed. 
     
     
       6. The friction stir welding method according to  claim 1 , further comprising:
 disposing a termination tab member formed of a 1000 series, 3000 series, 6000 series or 8000 series aluminum alloy in abutting contact with end faces of said joining portions of said first and second members on the side of termination of said friction stir welding operation; and 
 terminating said friction stir welding operation by successively moving said probe of said rotary tool from said joining portions of said first and second members into said termination tab member to form a continuous friction-stir-welded area extending across said joining portions and said termination tab member. 
 
     
     
       7. The friction stir welding method according to  claim 6 , wherein said termination tab member is a planar member having a length not shorter than four times a diameter of said shoulder members, in the direction of welding of said first and second members by said rotary tool, and a width not shorter than twice the diameter of said shoulder members, in a direction perpendicular to the direction of welding of said first and second members. 
     
     
       8. The friction stir welding method according to  claim 6 , wherein said termination tab member has a thickness not larger than a half of a diameter of said probe of said rotary tool.